Recently, a battery-powered portable electronic device such as a notebook personal computer (PC) and the like has become widespread. Such electronic devices are often equipped with a keyboard having a backlight in order to improve operability in the dark. The backlight of the keyboard is hereinafter referred to as a keyboard backlight. Generally, the keyboard backlight is turned on if the keyboard is operated and turned off if the keyboard is not operated for a certain period. While the keyboard backlight is on, the brightness of the keyboard backlight is generally maintained at a brightness level set by a user.
It should be noted that the energy consumed by the keyboard backlight forms a relatively large proportion of the energy consumed by the entire electronic device. Therefore, if the electronic device is powered by a battery, the lighting of the keyboard backlight greatly affects the operating time of the electronic device.
One reason for needing the keyboard backlight is that the user should check the position of the keys of the keyboard in the dark. After checking the position of the keys, some users touch-type, i.e., operate the keyboard without looking at the keyboard. Even if the user does not touch-type, the need to keep the keyboard backlight bright is small because the user's eyes adjust to the dark with time.